1. Field of the Invention
The invention relates to the field of motor control, more particularly to a current control method and device for a motor that is operable in a generator mode.
2. Description of the Related Art
U.S. Pat. No. 5,519,294 discloses a torque control method and device for a brushless DC motor used in an electric motorcycle. The motor is operable in a first mode, wherein the motor rotates in a positive direction and has a positive torque, and a second mode, wherein the motor also rotates in a positive direction but has a negative torque. In the second mode, the motor can act as a generator for storing energy to a battery.
In the aforesaid patent, the current through the motor in either of the first and second modes is controlled by closing and opening selected ones of a plurality of control switches of a switching circuit. Because the control switches are opened or closed in a continuous manner without taking into account the actual rotational speed or the magnitude of the back electromotive force (back EMF) waves of the motor, there is a tendency that the current flow during operation of the motor in the generator mode will exceed the rated current of the control switches, thereby resulting in damage to the switching circuit.
Therefore, the object of the present invention is to provide a current control method and device for a motor so as to prevent damage to electrical components during operation of the motor in a generator mode.
According to one aspect of the invention, in a system that includes a battery, a motor, a switching circuit that interconnects the battery and the motor, a switch driving circuit that is connected to the switching circuit, and a controller that is connected to the switch driving circuit for controlling operation of the switching circuit in one of a first mode, wherein the motor is configured so as to draw power from the battery and wherein the motor rotates in a positive direction and with a positive torque, and a second mode, wherein the motor is configured so as to supply power to the battery and wherein the motor rotates in the positive direction and with a negative torque, a method of controlling current flow to the motor when the switching circuit is operated in the second mode, comprises the steps of:
detecting actual rotational speed of the motor; and
controlling the switch driving circuit to adjust duty cycle of control pulses provided by the switch driving circuit to the switching circuit in an inversely proportional relationship with respect to the actual rotational speed of the motor, thereby controlling the current flow to the motor to prevent damage to the switching circuit.
According to another aspect of the invention, in a system that includes a battery, a motor, a switching circuit that interconnects the battery and the motor, a switch driving circuit that is connected to the switching circuit, and a controller that is connected to the switch driving circuit for controlling operation of the switching circuit in one of a first mode, wherein the motor is configured so as to draw power from the battery and wherein the motor rotates in a positive direction and with a positive torque, and a second mode, wherein the motor is configured so as to supply power to the battery and wherein the motor rotates in the positive direction and with a negative torque, a method of controlling current flow to the motor when the switching circuit is operated in the second mode, comprises the steps of:
detecting actual magnitude of back electromotive force waves of the motor; and
controlling the switch driving circuit to adjust duty cycle of control pulses provided by the switch driving circuit to the switching circuit in an inversely proportional relationship with respect to the actual magnitude of the back electromotive force waves of the motor, thereby controlling the current flow to the motor to prevent damage to the switching circuit.
According to still another aspect of the invention, in a system that includes a battery, a motor, a switching circuit that interconnects the battery and the motor, and a switch driving circuit that is connected to the switching circuit, a device for controlling current flow to the motor comprises:
a controller adapted to be connected to the switch driving circuit for controlling operation of the switching circuit in one of a first mode, wherein the motor is configured so as to draw power from the battery and wherein the motor rotates in a positive direction and with a positive torque, and a second mode, wherein the motor is configured so as to supply power to the battery and wherein the motor rotates in the positive direction and with a negative torque; and
a speed sensor connected to the controller and adapted to detect actual rotational speed of the motor;
the controller being adapted to control the switch driving circuit to adjust duty cycle of control pulses provided by the switch driving circuit to the switching circuit in an inversely proportional relationship with respect to the actual rotational speed of the motor when the switching circuit is operated in the second mode, thereby controlling the current flow to the motor to prevent damage to the switching circuit.
According to yet another aspect of this invention, in a system that includes a battery, a motor, a switching circuit that interconnects the battery and the motor, and a switch driving circuit that is connected to the switching circuit, a device for controlling current flow to the motor comprises:
a controller adapted to be connected to the switch driving circuit for controlling operation of the switching circuit in one of a first mode, wherein the motor is configured so as to draw power from the battery and wherein the motor rotates in a positive direction and with a positive torque, and a second mode, wherein the motor is configured so as to supply power to the battery and wherein the motor rotates in the positive direction and with a negative torque; and
a back electromotive force detector connected to the controller and adapted to detect actual magnitude of back electromotive force waves of the motor;
the controller being adapted to control the switch driving circuit to adjust duty cycle of control pulses provided by the switch driving circuit to the switching circuit in an inversely proportional relationship with respect to the actual magnitude of the back electromotive force waves of the motor when the switching circuit is operated in the second mode, thereby controlling the current flow to the motor to prevent damage to the switching circuit.